1. Field of the Invention
The present invention relates to a time information transmitter-receiver and a time information transmission-reception integrated circuit for transmitting and receiving a signal including time information.
2. Description of Related Art
A standard radio wave including time information, that is, a time code is sent in each country (for example, Germany, England, Switzerland, Japan or the like). In Japan, long wave standard radio waves the frequencies of which are 40 kHz and 60 kHz respectively are sent from two transmitting stations in Fukushima and Saga. The time code included in the standard radio wave is sent by the frame the cycle of which is 60 seconds, for every occasion when the place of minute of the exact time is updated, that is, for every 1 minute.
In late years, a so-called wave clock for receiving a standard radio wave including such the time code to correct the current time data by the standard radio wave has been put to practical use. The wave clock receives the standard radio wave via a built-in antenna for every predetermined time. Further, the wave clock amplifies and modulates the received standard radio wave and decodes the time code. Thereby, the wave clock corrects the current time.
When this kind of wave clock is placed in a room, it is often impossible to receive the standard radio wave according to the installation location, for example, in a steel framed house or a basement. Accordingly, a time information transmitter-receiver such as a repeater for receiving the standard radio wave, and transmitting a relaying radio wave by modulating the time code of the received standard radio wave by a predetermined carrier wave, in order to reduce the limitation of the installation location for the wave clock, has been known. The wave clock receives the relaying radio wave transmitted from the repeater, when the reception circumstance for receiving the standard radio wave is not well. Thereby, the wave clock can certainly perform the time correction without limitation of the installation location.
The time information transmitter-receiver such as the repeater receives an external radio wave such as the standard radio wave or the relaying radio wave transmitted from another repeater, and transmits the relaying radio wave obtained by modulating the amplitude of a predetermined carrier wave by the time code. In the repeater, the frequency of the carrier wave at the occasion of the generation of the relaying radio wave to be transmitted is often the same as the frequency of the received external radio wave. In this case, the phase shift is generated between the relaying radio wave to be transmitted and the received external radio wave, by a filter or the like that the repeater comprises.
Therefore, in the wave clock for receiving the relaying radio wave transmitted from the repeater, the synthesized signal that the external radio wave and the relaying radio wave the phases of which are shifted to each other are superposed on each other. That is, when the carrier wave of the external radio wave is defined as “A sin ωt” and the phase shift of the relaying radio wave with respect to the external radio wave is defined as φ, the carrier wave of the relaying radio wave is given as “B sin (ωt+φ)”. Therefore, the received radio wave received by the wave clock is the signal given by the following formula (1)
                                                                                          A                  ⁢                                                                          ⁢                  sin                  ⁢                                                                          ⁢                  ω                  ⁢                                                                          ⁢                  t                                +                                  B                  ⁢                                                                          ⁢                  sin                  ⁢                                                                          ⁢                                      (                                                                  ω                        ⁢                                                                                                  ⁢                        t                                            +                      ϕ                                        )                                                              =                                                                                          A                      2                                        +                                          B                      2                                        +                                          2                      ⁢                                                                                          ⁢                      B                      ⁢                                                                                          ⁢                      cos                      ⁢                                                                                          ⁢                      ϕ                                                                      ⁢                                  sin                  ⁡                                      (                                                                  ω                        ⁢                                                                                                  ⁢                        t                                            +                      B                                        )                                                                                                                          wherein              ,                              β                =                                  tan                  ⁢                                                            B                      ⁢                                                                                          ⁢                      sin                      ⁢                                                                                          ⁢                      ϕ                                                              A                      +                                                                                          ⁢                                              B                        ⁢                                                                                                  ⁢                        cos                        ⁢                                                                                                  ⁢                        ϕ                                                                                                                                                    (        1        )            
That is, according to the above formula (1), the amplitude of the synthesized signal is decreased because of the phase shift φ of the relaying radio wave with respect to the external radio wave. Accordingly, the problem that there is possibility for deteriorating the receiver sensitivity of the wave clock all the more, has occurred.